Others held posters of Mao Zedong, branded with the mock-patriotic slogan "Chinese people should drink Chinese milk" -- a dig at the throngs of mainland shoppers who enter Hong Kong to buy its infant formula, which is viewed as safer than Chinese infant formula.

Yet there were signs that not everyone understood the protest. Though many onlookers were smiling or laughing, some pedestrians were confused, thinking that the protesters were actual Communist supporters.

"I thought they were real," gasped one onlooker to his companion.

Western tourists appeared the most bewildered.

"I have no idea what's going on," a British visitor told CNN, even as the marchers surrounded him.

Later, a few online commenters remarked that the protesters made Hong Kong look bad.

"They succeeded in nothing but making a mockery of themselves. One keeps wondering how low Hongkongers can go," wrote user "bolshoi" on the South China Morning Post.

Rising tensions

Tensions between mainland Chinese and Hong Kongers have steadily increased in recent years, as more Chinese nationals flood into the former British colony to buy everything from food items to apartment buildings.